The present invention generally relates to an improved system for cross coupling resonators.
Cavity resonator filter assemblies are found in the receive and transmit sections of a diplexer used in a communication system. A plurality of resonators are located within the filter assembly. Such an assembly has a housing including walls that form the sides of the assembly and other walls that separate some of a plurality of resonators from each other. A top plate is attached to the top of the walls so that the assembly forms a cavity.
Each resonator of the assembly represents a pole of the filter response. The filter allows electronic signals of certain frequencies, the bandpass, to pass through the filter, while blocking or attenuating electronic signals of other frequencies, the stopband. Fine tuning of the assembly is provided by turning screws that extend through the top plate at locations above the resonators. This changes the distance that the screws extend through the plate, and thus their distance from the resonators.
Major tuning of the range of stopband frequencies of the resonator filter assembly is accomplished by changing the coupling between the resonators or by changing the number of resonators. Resonators that are closer to each other have a higher coupling value than resonators that are farther apart. Furthermore, the walls between the resonators, which were discussed above, decrease the coupling between resonators.
The stopband of the filter assembly can be increased by either increasing the number of resonators or by cross coupling a first resonator to a non-adjacent resonator, i.e. a resonator that would not be the next resonator with respect to the natural path of current from the first resonator. However, when space is limited within a cavity resonator filter assembly, cross coupling the resonators is the only option.
U.S. Pat. No. 6,208,221 teaches the use of wire loops to inductively cross couple non-adjacent resonators. The loops are attached and electrically connected to a pair of spaced elevated areas of the diplexer that are adjacent to the resonators. A wire soldered directly to each of two resonators can also be used to cross couple resonators.
Human error during the assembly of the wire to the resonators can cause variations in the placement of the wire with respect to the resonators, variations in the locations where the wire loop is soldered to the resonators, and variations in the formations of the loop. These variations affect the amount of cross coupling, which causes variations in the stopband attenuations. Therefore, what is needed is a cross coupler that provides a consistent and repeatable cross-coupling value between resonators.
This invention is directed to a novel system for inductively cross coupling resonators. Two resonators are interconnected by a cross coupler with a hole at each end. The holes secures each end of the cross coupler to one of the resonators.
The use of a stamped piece as a cross coupler results in a repeatable placement between resonators that minimizes any variation in coupling between resonators due to human error during assembly. This repeatability reduces assembly time and assembly cost.